The distribution of aminoterminal propeptides of type-III procollagen (indicating the presence of type-III pN-collagen, i.e., type-III collagen molecule with a non-cleaved aminoterminal propeptide), laminin and type-IV collagen was studied by immunohistochemical methods. The results were compared with the distribution of reticular fibres using Gomori's reticulin stain. Lymph nodes from 20 cases of Hodgkin's disease (HD) and 3 spleens affected by nodular sclerosis HD were studied. The reticular fibres stained for all the antigens investigated, the strongest reaction being for pN type-III collagen. Thick fibres stained mainly for type-III pN-collagen, the BM proteins being located in a fragmented rim on the surface. The distribution and composition of fibres was similar in both nodal and extranodal infiltrations. The morphological alterations noted in the fibres comprised (1) compression between nodules in the nodular type of lymphocyte-predominant HD, and (2) fragmentation, present in collections of histiocytes in lymphocyte-predominant HD. BM proteins and type-III pN-collagen were present in the walls of the sinuses and vessels. The marginal sinuses were often partially spared in spite of extracapsular invasion. Our results suggest that laminin, type-IV collagen and type-III pN-collagen are important components of reticular fibres in HD and that the composition of the fibres is similar to that seen in the normal lymph node.